Optically functional coated substrates are known. An optically functional coating is a coating aims at controlling optics, e.g. UV blocking or and anti-reflective coatings. For example, optically functional coated plates are used in architectural glass, horticultural glass, solar panels, picture frames glass, display glass (e.g. museum glass), electronic display glass (e.g. LCD display glass) and the like. A prototypical example of an optical coating is an anti-reflective coating. Untreated float glass plates show a strong light reflection generally of about 10% when looking at the glass at a near normal angle (5° offset). This typically reduces the functionality and often the aesthetics of the substrate and is therefore unwanted.
Optical coatings are commonly applied using either so-called dry application techniques like sputtering or physical vapor deposition or wet application techniques, e.g. dip, spray or curtain coating.
In a dip-coating process, the glass plate is dipped in a container with a coating fluid, and withdrawn at a certain speed. This process is commonly used for the application of optical thin films. Although this process is more cost-efficient than a “dry” application technique, it is accompanied with a number of disadvantages: the process involves handling of large amounts of chemicals, the coating is applied to both sides of the glass which for some applications is unnecessary or even disadvantageous, the coating speed is relatively low (up to 1 m·min−1), the coatings show a gradient in thickness due to gravity and other typical non-homogeneities, e.g. side effects due to evaporation.
Wet processes that allow application of a coating on one side of the substrate at speeds comparable to dry processes, include spray or curtain coating. However, the resultant coatings are typically very inhomogeneous. In single-layer anti-reflective coatings, this manifests itself in form of reflection and colour differences leading to a reduction in aesthetics and functional performance of the coated article.
In WO99/42860, a multilayer antireflective coating is applied using direct current spluttering or chemical vapor deposition (CVD). A protective polymer layer is then applied using a slot coater. A problem with this technique is that the optical coating is required to be applied in several layers using a dry technique (e.g, spluttering or CVD), with an additional protective wet layer applied. This technique is complex and expensive, in terms of coating equipment costs and running costs.
In JP2004-354601, the coating of a photosensitive film with a coating composition comprising a photo-sensitive resin and a non-volatile content of between 10 wt % and 25 wt %. After coating, the coated substrate is dipped in an alkaline developing solution to form the desired black matrix. A problem with this technique is that it may only be used at a coating speed of less than 200 mm/sec or less (12 meters per minute or less) due to the contamination of air bubbles in the film.
In WO07/093342, the application of an anti-reflective layer using a slot coater was disclosed in which a wet film thickness of between 1 and 5 μm was directed. Although this process provided an anti-reflective coating, further improvements are required in regard to the minimizing the variation in thickness and increasing the speed of application.
The aim of the present invention is to provide a wet process for applying an optical coating to a substrate and the product thereof, which at least partially overcomes the abovementioned pitfalls.